nix-config/modules/top/classes/nixos.nix

{
  lib,
  inputs,
  config,
  ...
}:
let
  inherit (lib)
    mapAttrs
    flatten
    unique
    optionals
    optional
    ;

  allRoles = config.dendritic.roles;
  allFeatures = config.dendritic.features;

  resolveRoles =
    let
      go =
        seen: roleName:
        if builtins.elem roleName seen then
          throw "Circular dendritic role reference detected: ${
            builtins.concatStringsSep " -> " (seen ++ [ roleName ])
          }"
        else
          let
            role = allRoles.${roleName} or null;
          in
          if role == null then
            throw "Unknown dendritic role: ${roleName}"
          else
            [ roleName ] ++ flatten (map (go (seen ++ [ roleName ])) role.roles);
    in
    roleNames: unique (flatten (map (go [ ]) roleNames));

  resolveFeatures =
    let
      go =
        seen: featureName:
        if builtins.elem featureName seen then
          throw "Circular dendritic feature reference detected: ${
            builtins.concatStringsSep " -> " (seen ++ [ featureName ])
          }"
        else
          let
            feature = allFeatures.${featureName} or null;
          in
          if feature == null then
            throw "Unknown dendritic feature: ${featureName}"
          else
            [ featureName ] ++ flatten (map (go (seen ++ [ featureName ])) feature.features);
    in
    featureNames: unique (flatten (map (go [ ]) featureNames));

  mkHost =
    hostName: host:
    let
      username = if host.primaryUser == null then null else host.primaryUser;

      user = if username == null then null else config.dendritic.users.${username};

      userHome = if user == null then null else user.homes.${hostName} or null;

      resolvedRoleNames = resolveRoles host.roles;
      roleFeatureNames = flatten (map (roleName: allRoles.${roleName}.features) resolvedRoleNames);
      resolvedFeatureNames = resolveFeatures roleFeatureNames;

      featureNixosModules = flatten (
        map (featureName: allFeatures.${featureName}.nixosModules) resolvedFeatureNames
      );

      featureHomeModules =
        if userHome == null then
          [ ]
        else
          let
            resolvedHomeRoleNames = resolveRoles userHome.roles;
            homeRoleFeatureNames = flatten (
              map (roleName: allRoles.${roleName}.features) resolvedHomeRoleNames
            );
            resolvedHomeFeatureNames = resolveFeatures homeRoleFeatureNames;
            embeddedHomeFeatureNames = builtins.filter (
              featureName: allFeatures.${featureName}.includeInEmbeddedHomeManager
            ) resolvedHomeFeatureNames;
          in
          flatten (map (featureName: allFeatures.${featureName}.homeModules) embeddedHomeFeatureNames);
    in
    inputs.nixpkgs.lib.nixosSystem {
      system = host.system;

      specialArgs = {
        inherit inputs;
      };

      modules = [
        {
          nixpkgs.overlays = [
            inputs.self.overlays.default
          ];
        }
        ../inventory/current.nix
        ../inventory/features.nix
        ../inventory/hosts.nix
        ../inventory/users.nix
        ../../aspects/roles.nix

        {
          dendritic.current = {
            inherit hostName;
            primaryUser = username;
          };

          networking.hostName = hostName;
        }
      ]
      ++ host.nixosModules
      ++ featureNixosModules
      ++ optional (username != null) {
        users.users.${username} = {
          isNormalUser = true;
          extraGroups = host.primaryUserExtraGroups;
        };
      }
      ++ optionals (user != null) user.nixosModules
      ++ optional (userHome != null) inputs.home-manager.nixosModules.home-manager
      ++ optional (userHome != null) {
        home-manager.useGlobalPkgs = true;
        home-manager.useUserPackages = true;

        home-manager.extraSpecialArgs = {
          inherit inputs;
        };

        home-manager.sharedModules = [
          ../inventory/current.nix
          ../inventory/features.nix
          ../inventory/hosts.nix
          ../inventory/users.nix
          ../../aspects/roles.nix
        ];

        home-manager.users.${username}.imports = [
          {
            dendritic.current = {
              inherit hostName;
              primaryUser = username;
            };
          }
        ]
        ++ user.homeModules
        ++ featureHomeModules
        ++ userHome.extraModules
        ++ [
          {
            home.username = user.username;
            home.homeDirectory = "/home/${user.username}";
            home.stateVersion = userHome.stateVersion;
          }
        ];
      };
    };
in
{
  config.flake.nixosConfigurations = mapAttrs mkHost config.dendritic.hosts;
}